Cover Story
Up to the task?
Natural gas engines have been with us for years. Is there any market for them in long-haul service?

By Jim Park
Special to Land Line


The problem with diesel fuel is that it’s so darned efficient, inexpensive (relatively) and readily available. It’s been terribly difficult to replace.

As engineers tinker with blends of exotic oils and volatile chemicals in search of diesel fuel’s replacement, natural gas has been efficiently and inexpensively powering diesel-type engines in many different applications, from transit buses to garbage trucks.

Now, even heavy-duty long-haul highway trucks are using abundant, clean, domestically produced natural gas as a fuel source.

The Holy Grail of diesel engine design is the clean and inexpensive-to-operate on-highway engine. These engines consume large quantities of fuel, making the cost of the fuel source a prime concern. Natural gas is a winner in that regard, but it comes with additional baggage that until recently has limited its widespread use.

First, it’s a gas, so it’s difficult to store in sufficient quantities. Second, its thermal efficiency isn’t equal to diesel, so 1.7 times as much natural gas (by volume) is required to pack the same punch as diesel. And third, it won’t self-ignite at current in-cylinder temperatures.

Natural gas engines have been in service for a number of years and have proven themselves technically reliable, efficient, and significantly cleaner running than traditional diesels. While their cost of operation can actually be lower than traditional diesels, the increased upfront costs push them outside the traditional trucking business model.

Enter a company called Westport Innovations Inc., based in Vancouver, BC, on Canada’s west coast. Through its different divisions and in partnership with Cummins Engine Co., Westport has developed two distinctly different natural gas engines that are proving their worth in trucking applications right now – a medium-duty, spark-ignited, 8.9-liter engine built on the Cummins ISL platform, and a heavy-duty, “dual-fueled” 15-liter Cummins ISX that runs on about 95 percent natural gas (see Page 87).

Westport Innovations Inc. is the common denominator in the LNG discussion, but there are two different corporate interests at the table. Cummins Westport Inc. (CWI) is a joint venture between Cummins and Westport Innovations. This group makes the medium-duty spark-ignited natural gas engine that powers the Sterling trucks recently rolled out at the Ports of Long Beach and L.A., in addition to engines used in transit buses, trash collection trucks, delivery vehicles, school buses, etc. The joint venture was established in 2001. Currently, more than 17,000 such engines are in service worldwide.

Westport Innovations itself manufactures a high-pressure direct-injection (HPDI) natural gas fuel system used on the Cummins ISX heavy-duty engine. It’s more than an add-on, but very few additional modifications are required to get ISX diesel performance, power, and fuel economy from liquefied natural gas fuel.

One of Westport’s first customers was Norcal Waste Systems of San Francisco. They operate a long-haul waste transfer operation, running 80,000-lb GVW on a 120-mile round trip to a landfill site six times a day.

 “Some of those trucks are approaching the 750,000 mile mark, with nearly 2 million miles logged across the fleet since 2000,” says Brian Zehr, manager of Westport’s customer care group.

Target applications
For the moment, natural-gas-powered trucks remain tethered to a fuel supply, and limited in range by capacity of the fuel tanks. LNG is stored at very cold temperatures and under pressure, so it requires a specialized distribution network and refueling facilities. This, obviously, limits the type of applications that LNG-powered trucks can serve.

 “They are best suited to service where the truck returns to the terminal at the end of a driving shift for refueling,” says Tony Picarello, Westport’s vice-president of fuel systems. “Range is dependent on fuel capacity. The ISX, for example, can run about 300 miles on a single tank of fuel. Pound for pound, you can’t go as far on LNG as you can on straight diesel.”

So, is there potential in the near future for long-haul over-the-road life for an LNG truck? According to Picarello, there is, although in a modified application.

 “Fleets are looking at different ways of getting goods across the country, and some are looking at the hub-and-spoke model as one that improves driver retention. We can relay a trailer across the country in much the same way some of the LTL carriers do business,” he says. “The fleets would put fueling stations at some of their terminals, and LNG tractors would run between terminals where fuel is available.”

There are no practical limits on the potential applications for LNG-powered trucks. They will work as well as a diesel in any heavy-duty application, but capital costs are higher. Picerallo maintains the lifecycle cost of running LNG can be lower than diesel.

 “We saw price differentials in 2008 of almost $2 per gallon less than diesel,” he says. “Pound for pound, LNG is much less expensive then diesel, and that’s where fleets can save a lot of money, in addition to running a much cleaner engine.”

The left seat view of LNG
Emissions improvements aside, any new engine must still pass the litmus test of performance under pressure – that is, driver satisfaction.

I had a chance to drive an ISX HPDI engine back in November 2005 while Westport Innovations was field-testing four units in fleet service running between Toronto, Ontario, and Flint, MI. Loads ranged from 100,000 to 140,000 pounds GVW. My load grossed out at 102,760 pounds, so the engine got a decent workout.

I noticed right from startup that it was quieter than a traditional ISX, which is fairly quiet to begin with. It was consistently quieter through the various operating ranges, even under full load pulling 75,000 pounds of beer up the two modest hills on Highway 401. It also seemed to idle more smoothly.

It didn’t lack the ISX’s usually lively throttle – a clue that the fueling system modifications had been done carefully to maintain the engine’s operating characteristics. It pulled as strong as one might expect from a 450-hp engine with 1,650 lbs.-ft. of torque. But it lacked the snort of a diesel – which is to say, the throttle didn’t seem quite as aggressive as a diesel’s.

The power rolled on more smoothly than I expected. Acceleration from a stop was more than satisfactory, and running up through the 10-speed gearbox was just like any other ISX, except quieter. The torque was there, and where I expected it to be, in the 1,200-1,300 rpm range.

I’ve also had a few chances to drive a Cummins Westport Inc. ISL-G under load, though not in revenue service.

The first was in August ’08 when Daimler Trucks North America arranged a trade media visit at Napa, CA, for the launch of the DD13 engine and an introduction to the Sterling LNG chassis. My second opportunity came in December ’08 at a media event at the Port of Long Beach when DTNA was celebrating the funding deals tailored to make LNG trucks affordable to fleet operators based at the port.

At 320 hp with 1,000 lbs.-ft. of torque, I didn’t expect it to set the world on fire, but it did an admirable job with the 65,000-pound load we dragged around Napa Valley’s wine country for a few hours that afternoon.

The truck was equipped with an Allison six-speed automatic transmission, and I suspect that had much to do with the perky feel of the engine. It had no shortage of get-up-and-go at the higher revs, but with only 1,000 lbs.-ft. of torque, it didn’t take kindly to lugging. The Allison prevented that most of the time anyway.

The ISL-G wasn’t a noisy engine either, but it sounded different – and a little less rattley – from diesel ISLs I’ve driven. Acceleration was good for the power and weight, but the six-speed transmission tended to take the revs a little high for my taste. It handled the few hills we hit well, but again, it didn’t lug down the way we’ve been taught to do modern diesels.

All in all, my limited experience with natural gas powered trucks leads me to think they are a suitable and adequate alternative to diesel engines. And knowing that driving one I’d be contributing to a 30-ton reduction in greenhouse gas emissions per truck over a year compared to a diesel, I’m more than prepared to give them the benefit of the doubt. LL


Editor’s Note: Jim Park is the former editor of Canada’s highway STAR magazine, and a founding member of the Owner-Operator Business Association of Canada. He spent 20 years on the road as a driver and owner-operator before becoming a journalist.